Abstract: A drying and mixing plant is provided comprising a tapered inner drum (1) and an oppositely tapered outer drum (4) attached together concentrically and rotated as a unit. A burner (37) directs a hot air stream into the small end (2) of the inner drum (1). Material is fed into the small end of the inner drum, where impellers (40) lift it and drop it into the hot air stream and move the material through the inner drum (1) aided by the downward taper of the inner drum. The material exits the inner drum and enters the outer drum (4) where an additive material is introduced and mixed with the material (42) as both move through the chamber (28) between the inner and outer drums to a material outlet. The receiving end (5) of the outer drum (4) is enclosed in a shroud (12), therefore the air stream is directed through the chamber (28) between the drums, the chamber having an expanding cross section which slows the air down allowing fines to precipitate out.